In the field of flat panel displays, self-emitting display devices with each pixel composed of a current-driven light-emitting device are gaining in popularity. A self-emitting display device features good visibility as well as excellent dynamic imaging characteristics. Among the current-driven light-emitting devices, light-emitting diodes (LEDs) are particularly well known.
Generally, a display device has a plurality of pixels arranged in a matrix, which are successively driven using dot-sequential or line-sequential scanning and are supplied with a display current. They provide a brightness corresponding to the display current supplied during the driving until they are driven next time. The display current received by the pixels is typically an analog current to achieve gray-scale display. The analog current is set at levels between the maximum and minimum brightnesses for each emitting device such that it can provide gray-scale display.
Thus, a display device including a current-driven light-emitting device requires a current supply circuit that accurately generates a display current corresponding to image data indicating brightness in gray-level for each pixel. In general, image data is digital data with a plurality of bits.
A current supply circuit in such a display device for supplying a display current for gray-scale display (hereinafter also referred to as “gray-scale current”) is disclosed in, for example, Japanese Patent Laying-Open No. 11-212493 (hereinafter referred to as “conventional art”), FIG. 1. A current supply circuit according to the conventional art uses thin film transistors (TFTs) which are selectively turned on/off in response to a plurality of bits composing image data to connect a plurality of constant-current supplies in parallel to generate a gray-scale current, which is the sum of supply currents from these constant-current supplies.